Typically, a solid oxide fuel cell (SOFC) employs a solid electrolyte comprising ion-conductive solid oxide such as stabilized zirconia, for example. The electrolyte is interposed between an anode and a cathode to form an electrolyte electrode assembly. The electrolyte electrode assembly is interposed between separators (bipolar plates). In use, normally, predetermined numbers of the electrolyte electrode assemblies and the separators are stacked together to form a fuel cell stack.
As the fuel gas supplied to the fuel cell, normally, a hydrogen gas generated from hydrocarbon raw material by a reformer is used. In general, in the reformer, a reformed raw material gas is obtained from hydrocarbon raw material of a fossil fuel or the like, such as methane or LNG, and the reformed raw material gas undergoes steam reforming, partial oxidation reforming, or autothermal reforming to produce a reformed gas (fuel gas).
As shown in FIG. 20 of the accompanying drawings, a reformer disclosed in Japanese Laid-Open Patent Publication No. 2006-273635, for example, has a lower plate 1a and an upper plate 2a. The lower plate 1a supports thereon a plurality of upwardly extending partition plates 3a, and the upper plate 2a supports thereon a plurality of downwardly extending partitions 4a, thereby defining a fluid passage 7a that is serpentine up and down and extends from a fuel inlet 5a to a fuel outlet 6a. 
Although not a reformer, Japanese Laid-Open Patent Publication No. 2008-117652 discloses a desulfurizer, which is similar in construction to the reformer, for use with a fuel cell. As shown in FIG. 21 of the accompanying drawings, the disclosed desulfurizer comprises a hollow cylindrical vessel 1b having a gas flow passage SP through which a fuel gas flows, partition plates 2b disposed as wall members and partition members in the gas flow passage SP, and a desulfurizing agent 3b which fills the gas flow passage SP.
Since the gas flow passage SP is segmented into a plurality of passageways by the partition plates 2b, the fuel gas which flows in the gas flow passage SP is also divided into a plurality of fuel gas streams and hence, uneven flow distribution of the fuel gas is prevented in the gas flow passage SP.
However, the reformer disclosed in Japanese Laid-Open Patent Publication No. 2006-273635 finds it difficult to meet minimum flow velocity requirements and tends to fail to prevent uneven flow distribution of the fuel gas, in a wide operating range. In addition, the disclosed reformer cannot absorb pulsation flows of raw fuel and hence cannot supply a reformed raw fuel stably.
If the desulfurizer disclosed in Japanese Laid-Open Patent Publication No. 2008-117652 is used as a reformer, then it also fails to meet minimum flow velocity requirements and is unable to prevent uneven flow distribution of the fuel gas, in a wide operating range from a partial load operation mode to a rated operation mode. In addition, the disclosed desulfurizer used as the reformer cannot absorb pulsation flows of raw fuel and hence cannot supply a reformed raw fuel stably.
If the gas flow passage SP is increased in length for a better reforming capability, then the reformer itself is increased in size (length) and cannot be made compact.